Strip of flat closures made of plastic foam that are coupled together

ABSTRACT

The invention relates to a strip (10) of flat closures (12) coupled together, made of plastic, wherein each closure (12) comprises a body (14) with an opening (16) therein for receiving and holding the access side (18) of a flexible packaging, as well as a slot (22), delimited by leg parts (20), which extends between the perimeter of the body (14) and the opening (16), and coupling parts (32a, 32b) for coupling to an adjacent closure, wherein the plastic is a plastic foam. A strip of this kind displays good fracture behaviour in existing closing machines.

The invention relates to a strip of flat closures made of plastic thatare coupled together. A closure of this kind comprises a flat body withan opening therein for receiving and holding the access side of flexiblepackaging, as well as a slot delimited by leg parts, which extendsbetween the perimeter of the body and the opening, and coupling partsfor coupling to an adjacent closure.

A strip of closures of this kind is known in this field (see for exampleNL1027149 for a strip of sealable bag closures of this type) and isemployed in closing machines for the closing of bags that are filledwith products, such as food products, for example bread etc. In a usualembodiment of a closing machine of this kind, the bags are pressedtogether on their access side to form a neck, and this neck is placedbetween brushes. Then the neck that is gripped between the brushes isbrought via a conveying element into the opening of a flat closure. Theflat closure is then broken off by machine from the strip of closuresthat are joined together. Flexible packaging can be closed with a bagclosure by machine in this way. The closing machines that are employedusually break the closures off by means of tensile force. See forexample EP0382169A1. Single closures of the same type, with or withoutcoupling parts, are also used in shops for manual packing of foodproducts.

The closures are “non-contaminating”, i.e. no loose parts such as thecoupling parts may arise in the machine during closure, especiallyduring breaking off, which could get into the packaging in the case of(food) products or could damage the packaging itself, bearing in mindhealth risks for the consumer, as well as quality and shelf life of the(food) product.

The applicant is marketing a strip of bag closures of this kind,manufactured from high-impact polystyrene (HIPS). The HIPS used has arelatively low tensile strength of about 21 N/mm² (measured according toNEN-EN ISO 527-3) and a relatively high elongation of about 77%. Thismaterial displays the desired fracture behaviour in the existingmachines. In practice, however, the closures still break off relativelyquickly, which is experienced as a disadvantage by the user. A toughermaterial is desired for the user. However, experience has taught thatHIPS can scarcely be further improved with respect to performance, inparticular with respect to elongation/strength ratio. If the material ismade tougher by modification, the tensile strength decreases.Conversely, if the tensile strength is increased, the toughnessdecreases.

Furthermore, there is inadequate availability of HIPS in the desiredthickness and dimensions for bag closures, so that the cost price of theclosures is relatively high. A further disadvantage is that bag closuresmade of HIPS are not easily sealable.

Thus, there is a need for bag closures made of materials other thanHIPS, which can be processed on existing closing machines, in which theclosures are detached in the machines by means of tensile force. Inother words the fracture behaviour (combination of tensile strength,toughness/stiffness) must be suitable for the breaking-off mechanismused in the machines, wherein a closure, in which a bag neck is applied,is detached from the strip of closures by a striking or slidingmechanism. On the other hand the strip, in particular the coupling partsof the bag closures, should not be so friable that the closures alreadybecome detached from one another prematurely, for example during feedinto and through the machine.

The aim of the invention is to provide a strip of flat bag closures thatare coupled together, which can be processed in the closing machinesknown in this field.

Another aim is to provide a strip of this kind that is less expensive.

Accordingly, the invention relates to a strip of flat closures made ofplastic that are coupled together, wherein each closure comprises a bodywith an opening therein for receiving and holding the access side offlexible packaging, as well as a slot delimited by leg parts, whichextends between the perimeter of the body and the opening, and couplingparts for coupling to an adjacent closure, wherein the plastic is aplastic foam, in particular a polyester foam, preferably a foamedamorphous polyethylene terephthalate.

Tests with strips of closures linked together of usual dimensions, whichwere made by stamping from sheets of foamed amorphous polyethyleneterephthalate (also known commercially as APET), displayed the desiredbrittle fracture behaviour and non-contaminating fracture behaviourwithout excessive (plastic) deformation in ordinary closing machineswith the action of tensile force for breaking off, such as are employedin bread factories and bakeries.

Polyethylene terephthalate (PET) is a plastic that is widely availablecommercially and that is still the subject of much development. However,PET cannot be used for bag closures of this type, because in the usualdimensions it is too strong for breaking-off in the existing machines. Ahigh tensile strength of about 56 N/mm² (measured according to NEN-ENISO 527-3) at a high elongation of about 100% makes a sheet of amorphousPET unsuitable for bag closures. Weakening by reducing the thickness isnot possible because thinner bag closures cannot be processed on theexisting machines. In addition, even these thinner bag closures arestill too strong. Furthermore, PET has a higher specific gravity thenHIPS (1.35 versus 1.05), which is unfavourable from the viewpoint ofcost price (per amount by weight).

By starting from a plastic foam, in particular a polyester foam,preferably a foam of amorphous PET, the desired decrease in strengthrelative to unfoamed PET can be achieved (the tensile strength of foamedfilm from amorphous PET with a thickness of 0.8 mm is 22 N/mm²), and therequired fracture behaviour (toughness/stiffness) can be obtained.Sheets of PET foam can be manufactured in the required thicknesses byextrusion in the presence of a (physical/chemical) blowing agent. ThisAPET foam is available commercially from Buergofol, among others. Thestrip of closures can be made by stamping from the film.

An additional advantage is that a thermoplastic polyester foam, inparticular foam of amorphous PET, is better sealable then HIPS, so thata method for “tamper-proof” closure becomes possible, as described forexample in the aforementioned NL1027149C, wherein the leg parts arejoined together by heat treatment. This is simpler than an alternativemanner of sealing by applying a quick hardening, flowable adhesive suchas a thermoplastic on and/or in the slot.

Yet another advantage is that polyester, especially polyethyleneterephthalate, is more reusable then HIPS. Thus the PET foam waste, thatresults from stamping, can be reused in the production of fresh thinstarting sheets, from which the closures are manufactured.

Advantageously, the coupling parts are breakable-off by machine, morepreferably in machines that are based on tensile force.

Advantageously, the foam has a closed-cell structure.

Advantageously, the slot extends between the opening and a peripheralpart of the body of the closure extending parallel to the longitudinaldirection of the strip.

Also advantageously, the coupling parts are provided on the feed sideand opposite side of the body of the closure. Here, the feed side is theside of the closure that is fed into the machine first.

The thickness of the bag closure is usually in the range 0.6-1.5 mm,such as 0.8 or 1.2 mm.

The invention further relates to the application of a strip according tothe invention in machine packing of products, in particular foodstuffs,such as food products, in flexible packaging, wherein the access side ofthe flexible packaging, usually as a folded neck, is brought into theopening of a closure.

The invention also relates to a method for manufacturing a stripaccording to the invention, said method comprising the steps ofsupplying a film of plastic foam, in particular a thermoplasticpolyester foam, preferably a foamed amorphous polyethyleneterephthalate, stamping the strip of flat closures coupled together, andwinding the strip on a roll.

The invention is explained hereunder on the basis of the drawing, inwhich

FIG. 1 shows an embodiment of a part of a strip of flat closuresaccording to the invention made from foamed amorphous polyethyleneterephthalate.

FIG. 1 shows in top view a part of a strip 10 of flat bag closures 12. Aflat bag closure 12 comprises a body 14 of foamed amorphous polyethyleneterephthalate, in this embodiment with a central opening 16 forreceiving a folded neck 18 of a flexible packaging. Projecting parts 19of the body 14 extend into the opening 16 to allow the closure 16 togrip the neck 18, so that a fixed position of the closure 12 withrespect to the neck 18 is assured and the neck is gripped well. Theclosure 12 further comprises, between leg parts 20, a slot 22 thatextends from the entrance 24 on a longitudinal side 26, parallel to thelongitudinal direction of the strip 10, up to the opening 16. Theentrance 24 of the slot 22 is broadened on the longitudinal side 26, sothat inserting the neck 18 in the slot 22 is facilitated. The directionof movement of the strip 10 in the machine is indicated with arrow B.The feed side 28 of the bag closure 12 and the opposite side 30 are eachprovided with two coupling parts 32 a and 32 b located some distanceapart, wherein the coupling parts 32 a of closure 12 a are connected tothe coupling parts 32 b of the preceding closure 12 b. In the embodimentshown, the right closure with the neck therein (not shown) is broken offfrom the strip 10 by means of a striking motion of a hammer or pin ofthe closing machine in the direction indicated with arrow A.

1. Strip of flat closures coupled together, made of plastic, whereineach closure comprises a body with an opening therein for receiving andholding the access side of a flexible packaging, as well as a slotdelimited by leg parts, which extends between the perimeter of the bodyand the opening, and coupling parts for coupling to an adjacent closure,wherein the plastic is a plastic foam.
 2. Strip according to claim 1,wherein the plastic is a foam of thermoplastic polyester.
 3. Stripaccording to claim 1, wherein the plastic is a foam of amorphouspolyethylene terephthalate.
 4. Strip according to claim 1, wherein thecoupling parts are breakable by means of tensile force.
 5. Stripaccording to claim 1, wherein the coupling parts are breakable bymachine.
 6. Strip according to claim 1, wherein the foam has aclosed-cell structure.
 7. Strip according to claim 1, wherein the slotextends between the opening and a peripheral part of the body of theclosure extending parallel to the longitudinal direction of the strip.8. Strip according to claim 1, wherein the coupling parts are providedon the feed side and opposite side of the closure.
 9. Use of a stripaccording to claim 1 in machine packing of products, in particularfoodstuffs, such as food products, in flexible packaging, wherein theaccess side of the flexible packaging is brought into the opening of aclosure.
 10. Method of manufacturing a strip according to claim 1, saidmethod comprising the steps of supplying a film of plastic foam,stamping the strip of flat closures coupled together, and winding thestrip on a roll.
 11. Strip according to claiml, wherein the plastic is afoam of thermoplastic polyester or a foam of amorphous polyethyleneterephthalate and wherein the coupling parts are breakable by means oftensile force.
 12. Strip according to claim 11, wherein the slot extendsbetween the opening and a peripheral part of the body of the closureextending parallel to the longitudinal direction of the strip.
 13. Stripaccording to claim 11, wherein the coupling parts are provided on thefeed side and opposite side of the closure.